The present invention relates to a process for the manufacture of .beta.-hydroxybutyric acid and its oligocondensates from its polycondensates obtained by biosynthesis.
Numerous microorganisms are capable of synthesising polycondensates of .beta.-hydroxybutyric acid (poly-.beta.-hydroxybutyrates), and various techniques, such as extraction, are known for separating the poly-.beta.-hydroxybutyrates from the biomasses.
As .beta.-hydroxybutyric acid is a very valuable intermediate for the fine chemicals industry, various attempts have been made to synthesise it starting from its polycondensates obtained by biosynthesis. However, all the processes envisaged hitherto for this purpose exhibit the serious disadvantage of leading not to the acid itself but to its derivatives. These known processes therefore necessitate the subsequent conversion of these derivatives to the acid, which makes them too complicated and too expensive to be suitable for industrial use.
Thus, a first of these known methods consists in saponifying the poly-.beta.-hydroxybutyrates by means of an alkaline solution, so as to form alkali metal salts of .beta.-hydroxybutyric acid. This method possesses the additional disadvantage of resulting in the formation of large amounts of undesired by-products such as the salt of crotonic acid. A second method which has already been proposed consists in treating the poly-.beta.-hydroxybutyrates with anhydrous hydrazine, which makes it possible to obtain crystals of the hydrazide of D(-)-.beta.-hydroxybutyric acid, and this can only be converted to the acid using stoichiometric amounts of acids such as sulphuric acid or hydrochloric acid, the yields observed being furthermore very low. In accordance with a third known method, methanolysis is carried out and this gives oligocondensates in the form of methyl esters and also the methyl ester of the acid.